In general, a conversation system may be classified into an object directional system for achieving a specific object/service and a chat system for an everyday conversation. Nowadays, with the spread of mobile devices, a user can easily access a conversation management system for fun. Such a chat system becomes a meaningful system to a person having a short rest time, elderly people to which someone to talk to is necessary, and children accessing for a simple interest. A merit of a chat system may be that a user is more familiar with accessing a mobile device by housing a chat system in the mobile device. General technology of an existing conversation management system is as follows. In order to construct a system, a (user articulation)-(system articulation) pair is previously constructed, and in order to increase coverage, a developer directly manually writes a lexical pattern of each user articulation. Thereafter, upon actually executing a conversation, in order to output an appropriate response to a sentence that a user articulates, the conversation management system compares the user articulation one to one with previously constructed lexical patterns, searches for a most appropriate pattern, and sends a system articulation that is connected to the pattern as a response.